The sampling frame for the Study is New York State (NYS), exclusive of New York City. The Study, which began September 4, 2007, is designed to use a population-based sampling strategy to recruit and compare the development of a matched-exposure cohort of infants, i.e., infants identified from pregnancies conceived with the help of infertility treatment, as noted in the NYS Perinatal Data System, and infants who were conceived without such therapies. For the primary cohort, a total of 1,500 infants identified as having been conceived by infertility treatment (exposed) are to be enrolled as participants at 3-5 months of age (gestation-corrected, if necessary) and followed longitudinally until age 36 months (3 years), along with a cohort of 4,500 unexposed infants, frequency-matched for residence within a NYS Regional Perinatal Network and plurality of birth. All co-twins of Study participants are to be enrolled simultaneously and either their outcomes noted (e.g., stillbirth, neonatal mortality), or they are to be followed (secondary cohort) on the same schedule as Study participants, although the co-twins will not be considered as part of the primary cohort. All higher order multiples (triplets, quadruplets) are also to be enrolled and followed on the same schedule, regardless of exposure status. Assuming that approximately 25% of the birth outcomes from infertility treatment are twins or higher order multiples, the secondary cohort is expected to number about 1,750 (450 twin siblings of exposed and 1,300 twin siblings of unexposed infants) plus all higher order multiples. All infants are eligible for selection without regard to race, ethnicity or gender. The period of recruitment for the referent (primary) birth cohort is expected to last one calendar year.[unreadable] [unreadable] Parents of infants born in NYS will be asked to participate in the Study for three years by: (a.) completing an initial questionnaire about the pregnancy, including, for example, confirmation of infertility treatment, time-to-pregnancy, infant feeding, and other demographic and socioeconomic factors (i.e., maternal education, occupation) and confounders associated with motor and social development; (b.) completing a standardized screening instrument that addresses their childs motor and social development at chronologic or gestation-corrected ages 4, 8, 12, 16, 20, 24, 30, and 36 months; and (c.) providing information on the child's growth and medical history (e.g., illnesses, diagnoses of birth defects, major impairments). Information on growth and medical history will be assembled in journal format from physicians examination data. Records will be linked to other pertinent health records (e.g., early intervention programs, WIC, birth defect or cancer registries).